During completion of the wellbore the annular space between the wellbore wall and a casing string (or casing) can be filled with cement. This process can be referred to as “cementing” the wellbore. A lower plug can be inserted into the casing string after which cement can be pumped into the casing string. An upper plug can be inserted into the wellbore after a desired amount of cement has been injected. The upper plug, the cement, and the lower plug can be forced downhole by injecting displacement fluid into the casing string. Variations in pressure of the displacement fluid can be used to determine the location of the upper plug, the cement, and the lower plug. These variations in pressure can be small and may not always be detected or may be incorrectly interpreted. Knowing the position of the upper plug, and thereby the cement below it, can prevent damage to the well or other errors in the cementing process. For example, variations in the pressure of the displacement fluid when the lower plug gets trapped at an undesired location in the casing string can be incorrectly interpreted to mean the lower plug has reached its destination at a float collar at the bottom of the casing string. Knowing the location of the upper cement plug can increase the integrity of the well.